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Home Bio-Digesters: How to Convert Waste Into Cooking Fuel

By Tobias Roberts Rise Writer
Apr 2, 2020

Around the world, restaurants, farms, grocery stores, markets, and households waste an estimated 1.3 billion tons of food. That amounts to almost one-third of all the food produced each year, says the UN's Food and Agriculture Organization (FAO). This wastefulness is a serious ethical issue, given that 795 million people, nearly 13 percent of the world's population, are malnourished. Project Drawdown estimates that food waste accounts for almost 8 percent of all greenhouse gas emissions. These emissions come mostly through methane emissions produced when organic waste goes to municipal landfills.  

There are straightforward ways to cut back on your household's contributions to greenhouse gas emissions. You can build a compost pile in your backyard, invest in a simple vermicomposting bin. Or, where available, you can separate your organic and inorganic waste to support municipal composting and recycling operations. But what if we told you that the methane gas emitted from natural decomposition processes could also be "harvested" for use in your kitchen? Home bio-digesters are a fantastic example of an appropriate technology that can kill two birds with one stone. Not only do they reduce emissions associated with food waste, but they can also diminish our reliance on natural gas.

Below, Rise offers a review of a bio-digester on the market today. We explain how bio-digesters work and offer a few ideas for how homeowners can reduce their greenhouse gas emissions by incorporating a household bio-digester system.

Gas Stove

What Are Bio-Digesters Used For? 

Natural gas is one of the most abundantly used fossil fuels for home energy. Almost 47 percent of households in the United States use natural gas for their home heating needs. Similarly, more than one-third of all homeowners use natural gas ranges and stoves for their cooking needs. In terms of total electricity production, of the 4.12 trillion kWh of electricity generated by utility companies in the United States, 1.58 trillion of those kWh came from burning natural gas.

Although natural gas is a "cleaner" fossil fuel than coal or oil, it still contributes to an enormous amount of carbon emissions that are driving global climate change. Also, natural gas supplies are getting increasingly harder to locate and extract. Many fossil fuel companies are now investing in invasive fracking operations. These operations have led to enormous environmental damage. They have also contaminated valuable groundwater resources upon which millions of Americans depend.

Limiting our use of natural gas, then, is one way to reduce the carbon footprint of our homes. While homeowners could opt for an all-electric home, natural gas for cooking does offer savings on your monthly energy bill. Depending on the electricity prices in your state or region, natural gas cooktops and ranges might be up to 30 percent cheaper than electric cooking options. 

Many professional chefs recommend using natural gas for cooking as food tends to cook faster while also allowing for more control over the cooking process. Instead of relying on municipal-supplied gas that required fracking for extraction, homeowners can use their kitchen scraps to create gas for their cooking needs.

biogas digester infographic biostar renewables
Biogas Digester Infographic. Photo Credit: BioStar Renewables

What Are Bio-Digesters? 

Biogas is mainly a mixture of methane and carbon dioxide that is produced naturally during the decomposition of organic matter. Many homeowners might consider carbon dioxide and methane to be the evil culprits of global warming. However, it is crucial to understand that these gasses are released naturally during the chemical processes that govern the natural world. Our industrial society's continued extraction and burning of fossil fuels is the real culprit, as this has disrupted the delicate balance of gasses in our atmosphere.

Backyard Compost
Backyard Composter. Photo Credit: Home Depot

Biogas is a natural by-product of the process of anaerobic bacteria fermenting the biodegradable, organic matter into methane and carbon dioxide. Even if you are a religious backyard composter, your banana and potato peels will undoubtedly release some carbon dioxide and methane as they decompose. Bio-digesters allow homeowners to take advantage of this gas for their cooking needs. For homeowners who raise backyard chickens or other livestock, animal waste can also be safely added to the digester to increase the amount of gas produced.

WWF Biogas Cook Stove
Biogas Cook Stove. Photo Credit: WWF

How Do Bio-Digesters Work? 

As we mentioned above, home bio-digesters are designed to capture the naturally occurring methane and carbon dioxide gasses from organic matter decomposition. This gas can then be used for home cooking needs. Large scale production of biogas might eventually be able to replace upwards of 5 percent of the natural gas used by municipal power systems. In contrast, home bio-digesters offer more immediate and tangible benefits for homeowners interested in reducing their carbon footprint.

Barrel Bio-Digestor
Barrel Bio-Digestor in Kenya. Photo Credit: Sören Säf

Home bio-digesters are made up of several parts or processes. These include a collection space or tank, an anaerobic digester, a separate container to drain or collect the slurry, and a gas connection that will receive the gas and send it to your kitchen. In the simplest of designs, kitchen scraps or farm animal waste can be placed in a sealed 55-gallon plastic barrel. A set of tubing allows the gas to be transferred to a tube from a car tire. The tube inflates as gas accumulates and can then be sent to a burner on a stove.

Cooking with Biogas
Cooking with Biogas. Photo Credit: M. Wauthelet

Larger scale home bio-digesters have been successfully developed by aid and development agencies around the world. Instead of having to walk miles collecting firewood for their cooking needs, many rural communities in developing nations have benefitted from large bio-digesters. These systems allow women to collect manure from their cattle or pigs to produce biogas. The biogas is stored in large cylindrical tubes made from pond liner, and then that gas is used for their cooking needs.

The only by-product of home bio-digesters is a liquid or semi-solid slurry that can be used as a natural fertilizer for fruit trees, flowers, and lawns. They do require a water supply, as bio-digesters only work with anaerobic decomposition, which requires the presence of water. 

Anaerobic decomposition occurs best with warmer temperatures, which might reduce the amount of biogas produced for homeowners who live in areas with long, cold winters. Fortunately, some companies have designed home-scale bio-digesters that get around these problems. We will review one such company below. 

How Efficient Are Bio-Digesters? 

Home bio-digesters work by creating an ideal environment where bacteria can break down organic waste from your kitchen and yard. The devices will store and harness the energy for use in cooking on gas stovetops and ovens. There have been limited studies regarding the efficiency of bio-digesters. However, a 2016 academic study that evaluated the digestion efficiency in full-scale anaerobic digesters for wastewater treatment plants. This study found that the best-designed systems could operate at upwards of 70 percent efficiency.

The Environmental and Energy Study Institute (EESI) finds that when biogas replaces reliance on fossil fuels, the result can be a "carbon negative system." The study says that converting waste into heat, vehicle fuel, and electricity has many benefits. They surmise that greenhouse gas emissions and dependence on foreign oil imports can be reduced. At the same time, environmental quality can be improved, and local jobs can be created.

Homeowners that replace their natural-gas-powered stoves and ovens with a home bio-digester are making the transition towards a carbon zero home. Biogas essentially has zero net greenhouse emissions. This is because the carbon dioxide and methane released during burning/cooking were previously drawn down from the atmosphere when the organic matter was growing. 

How Much Energy Do Bio-Digesters Make? 

The big question for many homeowners is: "How much biogas will I need in able to cook sustainably?" The total amount of biogas produced by your bio-digester will depend on several factors. These include the design of the unit, the climactic conditions (remember than anaerobic decomposition works best at warmer temperatures), and, how much organic waste your household uses.

Cooking With Fresh Veggies

According to one user testimony, merely adding 2 kg (4.5 pounds) of kitchen scraps each day to a home bio-digester allowed the family to cook up to two meals per day with the biogas produced. Homeowners who cook with lots of fresh produce or those who have a reliable source of farm animal manure will be able to produce much more biogas.  

How Much to Bio-Digesters Cost? 

Handy homeowners could potentially build their own home bio-digester, especially if they live on a homestead where they raise cattle or pigs. Check out this video of a pig farmer producing an enormous amount of methane gas. However, there are also a few companies out there that manufacture and market home scale bio-digesters that are incredibly practical and easy to use.

Home Biogas 2
Home Biogas 2.0. Photo Credit: Home Biogas

Home BioGas has created a machine that can create a reliable supply of biogas for homeowners. Their Home BioGas 2 product is easy to install and use, costs $720 (not including shipping). They will begin distribution in July of 2020. DIY Installation only takes an hour. The product includes:

  • A biogas adapted stovetop
  • A 343-gallon digester tank
  • A 185-gallon gas tank with a mechanical pressure and release mechanism
  • 23 feet of piping allowing homeowners to find the ideal place for the bio-digester and still be able to pipe the gas for use in the kitchen easily
  • A gas filter to remove any odors

For homeowners who live in areas with cold winters, the company recommends using a water heater to help the bacteria continue creating biogas. 

Even if you can only use a bio-digester during the spring, fall, and summer, producing biogas from food and animal waste is a simple way to reduce your household's carbon footprint and reliance on fossil fuels.

Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: 2021-07-10T05:54:52+0000
Tobias Roberts

Article by:

Tobias Roberts

Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.